Well to solve this firstly we should calculate her average speed while she was going to work. Which comes out to be 45 miles per hour.
Now if her average speed while going home is half as fast as while coming to work was, the answer would be 22.5 miles per hour. So the average speed for the total journey would be the average for these two values. As the distance was same for both the journeys we can simply do 45 + 22.5 / 2 = 33.75 mph.